Roof bolts are well known in the mining industry and are extensively employed for consolidating the roof and providing anchoring points and support. Their use involves drilling a hole in the roof of the mine and inserting into the hole a resin filled cartridge. The resin filled cartridges are also well known and comprise a curable resin and a catalyst for the resin contained in a sausage-like skin. In the next step of the installation a bolt is inserted which pierces the skin and penetrates the resin. The bolt is then usually spun about its axis to mix the resin and catalyst and, once mixed, the resin cures and sets.
In some mines it is the normal practice to apply tension to the bolt after the resin has set. This may be done by providing a screw threaded portion on the bolt and screwing a-nut onto the threaded portion to abut an end plate until a certain predetermined torque is reached, which is normally 120 to 150 ft lbs. This results in tension between the bolt and the end plate.